Turbine blade for a water turbine with bi-directional flow

ABSTRACT

The invention relates to a turbine blade for a water turbine, comprising, at least over part of its length, a curved profiled element having a median line created point-symmetrically in relation to a point of symmetry on the chord of the profiled element, half-way down, in such a way as to form an S-shaped curve. The median line splits the profiled element into a first side and a second side. The invention is characterised in that the turbine blade comprises an overflow device between the first side and the second side of the profiled element.

The invention concerns a bi-directional flow turbine blade for a waterturbine, which preferably is used in an immersing power generationfacility for the production of energy from a bi-directional flow ofwater.

For energy production from a flow having a variable direction, such as atidal current, for example, by means of a free standing, propellershaped designed turbine, normally a tracking mechanism is used, whichturns a gondola having the turbines attached thereto towards thecurrent. If two substantially opposing main flow directions are present,such as is the case with the ebb and flow of a tidal current, then adirectional tracking of this type can be obtained with a shuttered orrotating device, which rotates the gondola from a first position to asecond position. The disadvantage, however, is that for a trackingmechanism of this type, massive rotational or shutter blinder systemsmust be used. Furthermore, if it is the case that the water turbinedrives an electric generator, a device must be provided that prevents atwisting of the power cable emerging from the electric generator.

In order to circumvent this problem, an overall tracking of the waterturbine by means of a pitch adjustment device, which causes a rotationof the turbine blades through 180° at the hub, can be used instead tocreate a device for bi-directional flow. However, a design of this typealso has disadvantages, because, with a propeller shaped turbine havingturbine blades extending radially outwards, typically lying on theupstream side of the retaining structure of the gondola for at least oneflow direction, there is a flow impediment reducing the degree ofefficiency. Furthermore, a pitch adjustment mechanism is structurallyelaborate and is disadvantageous, with respect to the necessity ofmaintenance, for immersing power production facilities for obtainingenergy from an ocean current.

As another alternative for creating a water turbine for a bi-directionalflow, it is proposed in WO 2006/125959 A1, that a double symmetricalprofile be selected as the profile contour for the turbine blades of arotary water turbine. For this, the chord line represents a first axisof symmetry. In addition, the profile is symmetrical along a midpointline, which is defined as being perpendicular to the profile chord at50% of the length of the chord. The result is a lens-shaped profile,which ensures identical profile contours for a bi-directional flow. Itis disadvantageous, however, that due to the doubled symmetry selectedfor the profile contour in comparison with a cambered profile that issubject to flow from one side, there is a lower degree of efficiency.Furthermore, there are disadvantages due to downstream flow separationsand an increased flow resistance of the turbine blades.

Furthermore, from document US 2007/0231148 A1, profiles that aresymmetrical about a point, having a camber, are known. These arecharacterized by a point of symmetry, which at the midpoint of theprofile length, lie on the profile chord, such that the point-symmetrydesigned median line follows an S-curve. The thickness distribution ofthe profile is selected such that it is symmetric to the midline. Inthis manner, the S-curve shaped profile improves the performancecoefficients and limits the thrust coefficients.

The invention assumes the objective of designing a turbine blade suchthat a bi-directional flow can be accommodated. This turbine bladeshould also be suitable for use in a propeller shaped turbine of animmersing power production facility, wherein the turbine blade per seshould be characterized by a high degree of efficiency and limitedlongitudinal torsion for a flow arriving from both sides.

The invention builds on the known point-symmetrical profiles having anS-curve shaped median line and a thickness distribution that issymmetrical over the midline of the profile. This profile is thenfurther developed such that an overflow device from one profile surfaceto the second profile surface is provided.

Due to the point-symmetrical profile shape, there is the risk forS-curve profiles of a flow separation at the downstream profilecomponents. In addition, strong torsion forces act on a turbine bladehaving a profile of this type. Through an overflow from the first to thesecond profile surface in the middle portion and/or the downstreamsurface region of the profile, there is the possibility of reducing thetendency towards flow separation, and due to the reduced torsion forces,of structurally simplifying the reinforcing of the turbine blade againsttwisting.

In addition, the turbine blade profile can be substantially adjusted tothe technical properties of the flow, without the need for followingcompeting structural mechanical requirements in the construction of theturbine blade. For this, elongated, slender profiles may be used, whichresult in a high glide ratio. In addition, the attachments of theturbine blade at the hub of the rotating unit have to accommodatereduced torques and can be correspondingly simplified structurally andin terms of the production technology.

According to a first embodiment, the overflow device comprises numerousoverflow channels, whose orientation is adjusted to the bi-directionalflow direction. For another embodiment variation, which can be used asan alternative or in addition to the overflow channels, the overflowdevice is formed by a divided blade profile. For this, there is at leastone partial section in the central region of the overall profile, atwhich point the thickness distribution along the S-curve shaped medianline assumes the value of zero.

For a further development, the overflow device may comprise adaptivewall components, which, depending on the direction of flow, change froma first setting to a second setting, thus creating deviations in thepoint-symmetry of the profile. By this means, a targeted overflow to theback, downstream side region of the profile can be effected, withoutresulting in a serious loss in efficiency. In this case, the adaptivewall components can be displaced by means of a dedicated actuator,either actively, or said components can be designed as passive, elasticcomponents, whose contour changes with the flow.

In another design alternative of the invention, the overflow devicecomprises overflow channels, which can be closed, depending on the flowdirection. By this means, overflow channels can also be disposed outsideof the central region of the profile. The closing of the overflowchannels can be effected either passively or actively. For a passiveexecution, there is preferably a coupling of channel closing componentsin the overflow channels having elastic profile components, which aredisposed along the exterior of the profile that the current is flowingover, and become deformed by means of the flow forces. If a hydraulic orpneumatic working substance is accommodated in the elastic profilecomponents, then pressure for actuating the channel closing componentscan be generated and at the same time, an adaptive profile is createdthereby.

In the following, the invention shall be explained more precisely basedon embodiment examples in connection with the drawings, in which thefollowing is depicted:

FIG. 1 a shows a profile section, cut along the line A-A in FIG. 1 b,for a profile according to the invention, having a symmetry about apoint, with an overflow device from the first to the second profilesurface.

FIG. 1 b shows a partial section of a turbine blade from above, for theprofile from FIG. 1 a, having an overflow device applied in the centralregion of the profile, with a limited extension along the longitudinalaxis of the turbine blade.

FIG. 2 a shows as a profile section, an alternative embodiment exampleof the invention having numerous overflow channels.

FIG. 2 b shows a top view of a partial section of a turbine blade havinga profile in accordance with FIG. 2 a.

FIG. 3 a shows another profile section according to the invention,having off-center, passively controllable overflow channels.

FIG. 3 b shows a top view of a partial section of a turbine blade havinga profile in accordance with FIG. 3 a.

FIGS. 4 a and 4 b show a further development of the invention have apaired and point-symmetrical configuration of elastic components forinfluencing the profile in the overflow device from the first profilesurface to the second profile surface.

FIGS. 5 a and 5 b show active, adaptive wall components in the overflowdevice in different settings for the first and the second flowdirections.

FIG. 6 shows a point-symmetrical, cambered profile corresponding to theprior art, for the creation of a bi-directional flow turbine blade.

For the purpose of explaining the terminology used in the following,first a profile section corresponding to the prior art, depicted in FIG.6, shall be examined. A profile is shown, designed such that it ispoint-symmetrical in relation to the symmetry point 27. For this, thesymmetry point 27 is disposed on the profile chord 20 at the midpoint ofthe profile, and is, accordingly, covering the intersection of theprofile chord 20 at the midline 23, whereby the latter is defined asrunning perpendicular to the profile chord 20.

For the S-curve shaped profile, the median line 32, appliedsymmetrically in relation to the symmetry point 27, exhibits a camber w.Furthermore, the aforementioned condition of symmetry results in asymmetrically applied profile thickness distribution with respect to themidline 23. Other embodiments for bi-directional flow, point-symmetricalprofiles are conceivable (not shown), such as a median line having atleast one linear course in sections, in the central profile section andprofile tips 30, 31 designed such that they are point-symmetrical to oneanother.

For the following explanation, a conceptual division of the profilethrough the median line 32 is assumed, resulting in a first profilesurface 21, and a second profile surface 22. In addition, a division ofthe profile through the midline 23 into a first profile half 24 and asecond profile half 25, is to be assumed. For this, the first profilehalf 24 extends from the first profile tip 30 to the midline 23, and thesecond profile half 25, accordingly, extends from the midline 23 to thesecond profile tip 31.

Furthermore, for the indicated first flow direction 28, wherein aneffective flow is assumed, there is a suction effect in at least thefirst profile half 24 on the first profile surface 21, and there is apressure effect to the second profile surface 22. However, due to theS-curve in the region of the downstream edge of the second profile half25 on the first profile surface 21, i.e. in the vicinity of the secondprofile tip 31, a pressure node may occur for the observed first flowdirection 28, which reduces the efficiency of the profile, and furtherincreases the torsion acting on the S-curve profile. For the second flowdirection 29, the pressure and suction surface configuration isreflected over the symmetry point 27.

For the profile according to the invention, depicted as a profilesection in FIG. 1 a, there is a point-symmetrically applied overflowdevice 1, which is symmetrical in relation to the symmetry point 27. Inthe embodiment example depicted, the overflow device 1 interrupts theprofile at a central region 26, which is defined as that part of theprofile that extends from ⅜ to ⅝ of the profile length.

The overflow device 1 can extend, according to a first design,longitudinally over the entire turbine blade 13, such that there is adivided profile over the entire length. According to an alternative,presently depicted design, the overflow device 1 extends over a limitedsection of the length of the turbine blade 13. This design isillustrated in FIG. 1 b, which depicts a top view of the turbine blade13 having the profile according to the invention depicted in FIG. 1 a.For this, numerous overflow devices 1 can be provided along the lengthof the turbine blade 13, which are separated from one another bycross-bars, which improve the structural stability. These are not shownin detail in the figures.

The effect of an overflow device 1 provided according to the inventionfor a point-symmetrical, bi-directional S-curve profile subjected toflow is as follows: the substantial lift effect is caused, for the firstflow direction 28, by the front profile section, i.e. the first profilehalf 24. Correspondingly, for a flow direction in the oppositedirection, i.e. in the direction of the second flow direction 29, thesubstantial effect of the profile is provided by the second profile half25, which is then upstream. By means of the overflow device 1 accordingto the invention, an overflow from the pressure side to the downstreamregion of the opposite profile surface is caused. Accordingly, a portionof the profile current is guided along the first profile half 24 on thesecond profile surface 22, via the overflow device 1, to the secondprofile half 25 on the first profile surface 21 for the first flowdirection, thereby reducing the danger there of flow separations on theone hand, and torque being applied to the turbine blade 13, on the otherhand.

Another design example of the invention is evident from the profilesection depicted in FIG. 2 a, cut along the line B-B in FIG. 2 b. Anumber of overflow channels 2, 2.1, 2.2, . . . , 2.n are depicted fordefining the overflow opening 1. According to FIG. 2 b, the individualoverflow channels 2, 2.1, 2.2, . . . , 2.n are disposed over the lengthof the turbine blade 13, parallel and offset to one another. For this,designs are also conceivable for the adjacent channels, oriented atangles to one another, or provided with branches. In addition, thecross-sections of the overflow channels 2, 2.1, 2.2, . . . , 2.n can bemodified. An embodiment alternative having slit shaped overflow channels2, 2.1, 2.2, . . . , 2.n is preferred. Embodiments of this type are notdepicted in detail in the figures.

Another design of the invention is depicted in FIGS. 3 a and 3 b. Theprofile section C-C in FIG. 3 a shows a first, off-center flow channel 5and a second off-center flow channel 6, which at least for portions oftheir lengths are disposed outside of the central region 26. The firstchannel closing components 7.1, 7.2 are provided for closing the firstoff-center overflow channel 5. For the illustrated first flow direction28, these are closed, such that no overflow occurs through the firstoff-center overflow channel 5, and thereby in the region of the firstprofile half 24, from the first profile surface 21 to the second profilesurface 22. This is different in the case of the second, off-centeroverflow channel 6. In this case, the second channel closing components10.1, 10.2, designated for the illustrated first flow direction 28, areopen, such that in the second profile half, the desired overflow fromthe first profile surface 21 to the second profile surface 22 results.

For the depicted design, a passive control of the first and secondchannel closing components, 7.1, 7.2, 10.1, 10.2 occurs. For this, afirst elastic profile component 8, comprising a pressure accommodatingworking substance, is compressed for the illustrated first flowdirection 28, by means of which, a connection is provided between thefirst channel closing components 7.1, 7.2 and the first elastic profilecomponent 8 via the first coupling channel 9. Accordingly, a compressionof the first elastic profile component 8, due to its location on thepressure side for the flow direction 28, results in an expanding of thebellows shaped channel closing components 7.1, 7.2 applied thereto, andthereby to the aforementioned flow interruption in the first off-centeroverflow channel 5. This is different in the case of the second elasticprofile component 11, which lies point-symmetrically opposite the firstelastic profile component 8, in relation to the symmetry point 27, andtherefore is on the suction side for the first flow direction 28.Accordingly, the second channel closing components 10.1, 10.2 arecontracted due to the liquid coupling via the second coupling channel12, and not impeding the second off-center flow channel 6. For the, notdepicted, second flow direction 29, the first elastic profile component8 is on the suction side, and the second elastic profile component 11 ison the pressure side, as a result of which, the first channel closingcomponents 7.1, 7.2 open the first off-center overflow channel 5, andthe second channel closing components 10.1, 10.2 close the secondoff-center overflow channel 6.

In FIG. 3 b, a top view of a turbine blade 13 having a profile accordingto FIG. 3 a is shown. It is evident that the first elastic profilecomponents 8, 8.1, . . . 8.n, which, in each case, are dedicated to afirst off-center overflow channel 5, 5.1, . . . , 5.n, have a limitedextension in the longitudinal direction of the turbine blade, in orderto prevent a transporting of the working substance through centrifugalforce.

As a result of the deformation of the elastic profile components 8, 8.1,. . . , 8.n, 11 caused by current forces, an adaptive adjustment of theprofile results, dependent on the direction of flow. This is understoodto be a breakdown of the point-symmetry as a result of the deformationof the profile, wherein the deformation direction is reversed with achange in the direction of flow.

FIGS. 4 a and 4 b show another design alternative of the invention, forwhich a first adaptive wall component 3 and a second adaptive wallcomponent 4 are provided for a further development of an overflow device1 corresponding to that in FIG. 1 a. For this, the first adaptive wallcomponent 3 is disposed in that part of the overflow device 1, that isdedicated to the first profile half 24 on the first profile surface 21.Respectively, the second adaptive wall component 4, dedicated to thesecond profile half 25 on the second profile surface 22, is located in apoint-symmetrical manner to this, reflected over the symmetry point 27.

The passive adjustment of the contour of the first and the secondadaptive wall components 3, 4 is shown in FIGS. 4 a, 4 b, which areconstructed as elastic components, or contain a filling that can adaptto the current, or can be compressed. Due to the deformation of theadaptive wall components 3, 4, a symmetry breakdown of the contour ofthe overflow device 1 occurs when the profile is subjected to a flow,which results in an improvement of the flow guidance in the overflowdevice 1. The basic contour of the profile, i.e. its state when notsubjected to flow, is not changed, however, in the point-symmetry inrelation to the symmetry point 27.

A design alternative having a first active, adaptive wall component 16and a second active, adaptive wall component 17 is shown in FIGS. 5 aand 5 b. For this, the first active adaptive wall component 16 isdedicated to the first profile half 24 of the first profile surface 21,and the second active, adaptive wall component 17 is a part of thesecond profile half 25 on the second profile surface 22. For theexecution of a rotational movement about a first center of rotation 14,which lies in the vicinity of the outer edge of the overflow device 1,the first adaptive wall component 16 has a dedicated first actuator 18,which may comprise a hydraulic cylinder, for example. For smalladjustments, piezo components can also be used as actuators 18.Accordingly, the second adaptive wall components 17 have a dedicatedsecond actuator and a second center of rotation 15.

For the first flow direction 28, depicted in FIG. 5 a, the secondactive, adaptive wall component 17 is extended, and corrects the overallcontour of the second profile half 25. The first active, adaptive wallcomponent 16 remains in the retracted state. When the flow is changed tothe second flow direction 29, then, accordingly, the first active,adaptive wall component 16 is extended and corrects the associatedprofile region. On the suction side, the second active, adaptive wallcomponent 17 remains in its original state. This situation is depictedin FIG. 5 b.

The embodiment according to FIGS. 5 a and 5 b uses active, added,adaptive wall components in the region of the overflow device 1according to the invention, wherein an increased technical expenditureis necessary for the control in contrast to a purely passive system.Compared to the active devices for the adaptation to a change in thedirection of flow by means of a complete rotation of the turbine blade13 using a pitch adjustment device applied at the intersection with thehub, that have been used until now, there is the advantage that by meansof numerous adaptive components that can be activated separately, anadaptation of the profile contour to the direction of flow can becaused, that can be distributed to numerous individual components forthe flow forces. In addition, if individual adaptive components cease tofunction, this does not result in a complete loss of function to theturbine blade 13.

Other designs of the invention are conceivable. As such, a channelstructure having an intake opening in the region of a profile tip can beapplied within the profile, for example, which displaces the flow partsalong the median line within the profile to an output opening in theregion of a downstream and suction side section of the profile. Otherdesign variations can be derived from the following Claims.

LIST OF REFERENCE SYMBOLS

-   1 Overflow device-   2, 2.1, 2.2, 2.m Overflow channel-   3 First adaptive wall component-   4 Second adaptive wall component-   5, 5.1, . . . , 5.n First off-center overflow channel-   6, 6.1, . . . , 6.n Second off-center overflow channel-   7.1, 7.2 First channel closing component-   8, 8.1, . . . , 8.n First elastic profile component-   9 First coupling channel-   10.1, 10.2 Second channel closing component-   11 Second elastic profile component-   12 Second coupling channel-   13 Turbine blade-   14 First center of rotation-   15 Second center of rotation-   16 First active, adaptive wall component-   17 Second active, adaptive wall component-   18 First actuator-   19 Second actuator-   20 Profile chord-   21 First profile surface-   22 Second profile surface-   23 Midline-   24 First profile half-   25 Second profile half-   26 Central region-   27 Point of symmetry-   28 First direction of flow-   29 Second direction of flow-   30 First profile tip-   31 Second profile tip-   32 Median line-   w camber

1. A turbine blade for a water turbine, having a cambered profile with amedian line (32) in at least a portion of its length, that is designedto be symmetrical about a point in relation to a point of symmetry (27)lying at the midpoint of the profile length on the profile chord (20),and forming an S-curve, wherein the median line (32) divides the profileinto a first profile surface (21) and a second profile surface (22), andwherein the profile comprises a midline (23) that depicts aright angleto the profile chord (20) having the symmetry point (27) as its startingpoint, and which divides the profile into a first profile half (24) anda second profile half (25), characterized in that the turbine bladecomprises an overflow device (1), which establishes a fluid connectionbetween the first profile surface (21) and the second profile surface(22), wherein the overflow device (1) comprises a first off-centeroverflow channel (5, 5.1, . . . , 5.n), which establishes a fluidconnection between the first profile surface (21) and the second profilesurface (22) in the first profile half (24), and a second off-centeroverflow channel (6, 6.1, . . . , 6.n), which establishes a fluidconnection between the first profile surface (21) and the second profilesurface (22) in the second profile half (25), and the first off-centeroverflow channel (5, 5.1, . . . , 5.n) has a dedicated first channelclosing component (7.1, 7.2) and the second off-center overflow channel(6, 6.1, . . . , 6.n) has a dedicated second channel closing component(10.1, 10.2), which are configured for the selective closing of therespective off-center overflow channels, depending on the direction offlow.
 2. The turbine blade according to claim 1, characterized in thatthe selective closing of the first off-center overflow channel (5, 5.1,. . . , 5.n) and the second overflow channel (6, 6.1, . . . , 6.n) arecaused by passive means.
 3. The turbine blade according to claim 2,characterized in that a first elastic profile component (8, 8.1, . . . ,8.n) on the second profile surface (22) is used for the passive controlof the first channel closing component (7, 7.1, 7.2), and a secondelastic profile component (11) on the first profile surface (21) is usedfor the passive control of the second channel closing component (10.1,10.2).
 4. The turbine blade according to claim 1, characterized in thatthe overflow device (1) comprises a first adaptive wall component (3)and a second adaptive wall component (4), which are disposedsymmetrically about a point of symmetry (27).
 5. The turbine bladeaccording to claim 4, characterized in that the first adaptive wallcomponent (3) and the second adaptive wall component (4) function aspassive components, the contours of which are affected by the flowforces.
 6. The turbine blade according to claim 4, characterized in thatthe first adaptive wall component (3) comprises a first active, adaptivewall component (16), and the second wall component (4) comprises asecond active, adaptive wall component (17).
 7. A method for operating aturbine blade for a water turbine with bi-directional flow, having acambered profile with a median line (32) in at least a portion of itslength, that is designed to be symmetrical about a point in relation toa point of symmetry (27) lying at the midpoint of the profile length onthe profile chord (20), and forming an S-curve, wherein the median line(32) divides the profile into a first profile surface (21) and a secondprofile surface (22), and the turbine blade comprises a first off-centeroverflow channel (5, 5.1, . . . , 5.n), which establishes a fluidconnection between the first profile surface (21) and the second profilesurface (22) in the first profile half (24), and a second off-centeroverflow channel (6, 6.1, . . . , 6.n), which establishes a fluidconnection between the first profile surface (21) and the second profilesurface (22) in the second profile half (25), and wherein the firstoff-center overflow channel (5, 5.1, . . . , 5.n) comprises firstchannel closing component (7.1, 7.2) and the second off-center overflowchannel (6, 6.1, . . . , 6.n) comprises second channel closing component(10.1, 10.2), and wherein, by means of the respectively dedicatedchannel closing component, depending on the direction of flow, theupstream off-center overflow channel is closed, and the downstreamoff-center overflow channel is opened.
 8. The turbine blade according toclaim 2, characterized in that the overflow device comprises a firstadaptive wall component and a second adaptive wall component, which aredisposed symmetrically about a point of symmetry.
 9. The turbine bladeaccording to claim 3, characterized in that the overflow devicecomprises a first adaptive wall component and a second adaptive wallcomponent, which are disposed symmetrically about a point of symmetry.